1. Field of the Invention
The present invention relates to resins for plastic lenses, and more particularly to resins for lenses which have a high refractive index and have a high impact resistance.
2. Related Art
Heretofore, a diethyleneglycol bisarylcarbonate resin has been widely used as a resin for plastic lenses. This resin has excellent impact resistance and transparency, and, at the same time, has good light-dispersion properties. However, the refractive index of the resin is as low as 1.50, so that in order to obtain refraction comparable to that of a glass lens, a lens made of this resin is necessarily made thick.
On the other hand, it is known that a variety of diacrylates and dimethacrylates can be readily polymerized radically to produce lenses of excellent transparency. For instance, it is known that resins for lenses which can be obtained from di(meth)acrylate having a bromine-containing bisphenol A skeleton (Japanese Laid-Open Patent Publications Nos. 184210/1984 and 193915/1984) or di(meth)acrylate having a sulfur-containing aromatic skeleton (Japanese Laid-Open Patent Publications Nos. 26010/1985 and 195357/1987) have well-balanced optical properties with a high refractive index and a high Abbe number.
However, although the above compounds form a highly-crosslinked structure when polymerized radically and show the properties of high resistance to heat and abrasion, the cured polymers tend to be brittle. As a means for improving the above shortcoming, a method in which use is made of a bromine-containing bisphenol A derivative (meth)acrylated and urethanized is disclosed in Japanese Laid-Open Patent Publication No. 51706/1985. However, since a bromine atom is contained, the compound thus obtained has a high specific gravity. For this reason, it is inevitable that the compound has poor weather resistance.